In Canada most places quoted me $120-130 for a 5lb steel cylinder filled, Kijiji can help or you can rent one from many welding gas shops for a pretty low fee ($4/month is what I'm paying).
You could also check out JL aquatics, I think they had an aluminum tank pretty cheap and orders over $100 have free Canadian shipping... they might be the cheapest that I've seen but then you have to find someplace to fill it, some suppliers won't fill tanks that they didn't sell/rent, some don't care.